This invention relates to locks and in particular locks suitable for securing a door, window or the like.
Chain-type locks are well known and have been used for many years to secure doors. The most common type of chain fastener has a short length of chain which is secured at one end to a door or door jamb by a suitable mounting plate. To the free end of the chain is fastened a locking bar which has an enlarged head. By inserting this head into a slot formed in another plate the lock can be secured. Both plates used in the standard chain-type lock are commonly fastened to the door or door jamb by means of ordinary screws. A common problem with such locks is that one of the plates can often be torn from the surface on which it is mounted by the application of sufficient force. Of course once one of the plates is torn loose, the door is free to open.
Early U.S. Pat. No. 242,568 issued June 7, 1881 to William Sparks describes a chain bolt having a small attachment plate to which the chain is attached and a larger plate having a hole therein which is almost circular except for two radially extending notches. A pendant lever is attached to the free end of the chain and it has a stud projecting from one side and having side projections thereon. When the stud is inserted into the opening in the larger plate, the lever will pivot under its own weight to lock the device.
U.S. Pat. No. 3,705,504 issued Dec. 12, 1972 to Dewey Johnson describes a chain door latch device adapted for use for inwardly and outwardly swinging doors having a latch bracket and a chain fastening member. The bracket is provided with an elongated slot with an enlarged opening at each end of the slot. The latch slide member which is fastened to the chain has mounted on its free end a matching enlarged member that is received by the enlarged openings in the bracket. The latch bracket is provided with a resilient member at the enlarged opening nearest the chain fastening member to prevent removal of the slide member therefrom.
U.S. Pat. No. 3,936,085 issued Feb. 3, 1976 to Donald Long describes a lock protector for wooden doors equipped with both the usual bolt or latch lock and a chain lock. There is provided a metal door plate of U-shape adapted to bridge the free edge portion of the door at the lock and apertured to pass the lock bolt. The chain is detachably connected to a chain plate which is strongly affixed to the door frame. The two metal plates provided are said to prevent the chain connections from being torn out by kicks or blows or pressure applied to the door. One problem with the described protector is that it is not designed to mount a chain lock on its own but is intended for use in conjunction with a standard bolt or latch lock.
It is an object of the present invention to provide a simple to use and inexpensive means for securely fastening a locking device to a door or door jamb. It is another object of the invention to provide a mechanism suitable for securely mounting a chain-type lock, the mounting plates for which are mounted on the inside surface of the door and door jamb.